Pilots generally rely on very high frequency (VHF) omnidirectional range (VOR) navigation systems, instrument landing systems (ILSs), and/or distance measuring equipment (DME) to aid with navigation and landing when flying during periods of low visibility or inclement weather. Generally, a VOR system is implemented by dispersing VOR transmitter facilities across a geographic area. VOR receivers, located on the aircraft, receive signals from VOR transmitters and help guide the aircraft through such geographic areas. The basic principle of operation of the VOR navigation system may include the VOR transmitter transmitting two signals at the same time. One VOR signal may be transmitted constantly in all directions, while another signal is rotatably transmitted about the VOR transmission facility. The airborne VOR receiver receives both signals, analyzes the phase difference between the two signals, and interprets the results as a radial to or from the VOR transmitter. Thus, the VOR navigation system allows a pilot to simply, accurately, and without ambiguity navigate from VOR transmitter facility to VOR transmitter facility. Each VOR transmission facility operates at a frequency that is different from the surrounding VOR transmitters. Therefore a pilot may tune the aircraft VOR receiver to the VOR transmission facility with respect to which navigation is desired.
The ILS is a ground-based instrument approach system that provides aircraft with lateral guidance (e.g., from localizer antenna array) and vertical guidance (e.g., glide slope antenna array) while approaching and landing on a runway. In principle, an aircraft approaching a runway is guided by ILS receivers in the aircraft that perform modulation depth comparisons of signals transmitted by a localizer antenna array located at the end of the runway and by a glide slope antenna array located to one side of the runway touchdown zone.
Generally speaking, two signals are transmitted by the localizer from co-located antennas within the array. One signal is modulated at a first frequency (e.g., 90 Hz), while the other signal is modulated at a second frequency (e.g., 150 Hz). Each of the co-located antennas transmits a narrow beam, one slightly to the left of the runway centerline, the other slightly to the right of the runway centerline. The localizer receiver in the aircraft measures the difference in the depth of modulation (DDM) of the first signal (e.g., 90 Hz) and the second signal (e.g., 150 Hz). The depth of modulation for each of the modulating frequencies is 20 percent when the receiver is on the centerline. The difference between the two signals varies depending on the deviation of the approaching aircraft from the centerline. The pilot controls the aircraft so that a localizer indicator (e.g., cross hairs) in the aircraft remains centered on the display to provide lateral guidance.
Similarly, the glide slope (GS) antenna array transmits a first signal modulated at a first frequency (e.g., 90 Hz) and a second signal modulated at a second frequency (e.g., 150 Hz). The two GS signals are transmitted from co-located antennas in the GS antenna array. The center of the GS signal is arranged to define a glide path of a predetermined slope (e.g., 3°) above the ground level for the approach of the aircraft. The pilot controls the aircraft so that a guide slope indicator (e.g., cross hairs) remains centered on the display to provide vertical guidance during landing.
In aviation, the basic objective for flight inspection of the various navigation aid systems has remained much the same for the last half a century. For example, flight inspection services (FIS) are provided by an agency such as the Federal Aviation Administration (FAA), and provide airborne flight check of electronic signals-in-space from ground-based navigational aid equipment that support aircraft departure, en-route, and arrival flight procedures. The flight check are conducted by a crew using a fleet of specially-equipped flight inspection aircraft.
Currently, for example, there are various flight maneuvers that must be performed by a flight inspection crew as part of a flight inspection of the various navigation aid systems. Each navigation aid system is inspected periodically, and requires an aircraft fleet that is expensive to maintain, an inspection crew to fly and maintain the aircrafts, ten or more hours of flight time to accomplish, and appropriate weather to perform the flight maneuvers (e.g., not too windy and with good visibility).
Therefore, there exists an unmet need in the art for methods, apparatuses, and computer-readable media to perform the flight maneuvers required to inspect navigational aid systems that reduces the expense of maintaining a fleet of aircraft, commissioning a crew, and which allow the maneuvers to be performed under less than ideal weather conditions.